1. Field of the Invention
The present invention relates to sensors, in particular pressure sensors.
2. Description of the Related Art
Pressure sensors have many-practical applications and may be used to detect that a person is sitting in a car seat or to detect an obstacle in the path of a mechanical moving part. For example, a motorised garage or lift door may be equipped with a pressure sensor on the leading edge. When an obstacle is detected, an input signal may be provided to the motor control from the sensor, which in turn may trigger the motor control to reverse the direction of motion of the moving door to prevent damage to the door and/or the obstacle. Applications may be safety-critical.
Different types of pressure sensor are suitable for such an application. These include pneumatic based sensors that utilise a tube and an air pressure sensor arranged to detect a change in the internal tube pressure. Wire based sensors utilise conductive strips located within a soft component and are arranged to detect contact between the strips. Optical based sensors utilise a hollow, flexible soft component, light transmission and a receiver arranged to detect light occlusion. Field based sensors utilise an antenna to establish an electrical field along the leading edge, arranged to detect the presence of a conductive object. Another type of sensor utilises a flexible surface incorporating push-button control switches, formed from layered conductive plastic or foil. A common problem with these types of sensors is that they display unsatisfactory durability. Applications for the above types of sensor are restricted by the limited ability of pneumatic, wire, optical and push-button switch based sensors to accommodate bends or curves around tight radii, and the difficulty of operating a field based sensor in a changing environment.